JPH06145850A - Hydrogen storage alloy and hydrogen storage electrode - Google Patents

Abstract

PURPOSE:To provide a hydrogen storage electrode having a high service capacity and a high discharge voltage by forming a hydrogen storage alloy with the La, Mn, Cu, etc., in a specified ratio and specifying the oxygen content of the alloy powder. CONSTITUTION:This hydrogen storage alloy is expressed by LmNiaCobAlcMd. In the formula, Lm is La-rich Mm the La in the Lm is controlled to 40-70mol%, 1.2<=a<=1.6, 0.1<=b<=0.4, 0.05<=c<=0.1, 0.1<=d<=0.3, and 1.8<=a+b+c+d<=2.4, and M is at least one kind among Mn, Cu, Zn, Ag, In, Sn and Pb. The oxygen content of the alloy powder is adjusted to 0.05 to 0.3wt.%. Consequently, hydrogen is electrochemically occluded and discharged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy capable of electrochemically storing and releasing hydrogen.

[0002]

2. Description of the Related Art Heretofore, a hydrogen storage alloy capable of electrochemically storing and releasing hydrogen has been known as AB _{5 type} L alloy.
Based on aNi ₅ , a practical system was found by substituting a part of the contents of La and Ni for other elements. This alloy system is excellent as an electrode and
When the Ni-hydrogen battery is combined with the i-electrode, a battery having 1.5 to 2.0 times the procedure of the conventionally used Ni-Cd battery can be manufactured, which has many advantages. . However, when a battery having a higher capacity is desired, an alloy called AB _{2 type in} which the A site is composed of Zr, Ti or the like and the B site is composed of Ni or V is disclosed in, for example, JP-A-64
No. 60961. Whereas the conventional AB ₅ alloy has a capacity of about 300 mAh / g, these AB ₂ alloys have a large capacity of 350 mAh / g or more. Higher capacity was expected.

[0003]

However, in the above conventional hydrogen storage alloy, the oxide film on the surface, especially the oxide film of zirconium is dense and difficult to pass hydrogen.
Due to the original characteristics of the hydrogen storage alloy, there was a problem that the voltage characteristics during discharge were poor. This is because most of the AB _{2 type} alloys have a large inclination of the plateau region of the hydrogen absorption curve as compared with the AB _{5 type} alloys, so that the discharge voltage changes greatly with the discharge time. For this reason, there has been a problem that the discharge capacity up to the final voltage range of 1.1 to 1.0 V, which is normally used in home electric appliances and the like, becomes almost the same level as that of the conventional alloy. An object of the present invention is to provide a hydrogen storage electrode having a high capacity and an excellent discharge voltage.

[0004]

In order to solve the above problems, the present invention provides a composition formula LmNi _a Co _b Al _c M _d in which the amount of La in Lm is 40 to 70 mol%, and a, b,
The ranges of c and d are 1.2 ≦ a ≦ 1.6, 0.1 ≦ b ≦ 0.
4, 0.05 ≦ c ≦ 0.1, 0.1 ≦ d ≦ 0.3, 1.
8 ≦ a + b + c + d ≦ 2.4, and M in the composition formula is M
This is to oxidize the powder of the hydrogen storage alloy composed of at least one of n, Cu, Zn, Ag, In, Sn and Pb by 0.05 wt% to 0.3 wt% with respect to the weight of the alloy. The hydrogen storage electrode is characterized in that a foamed nickel substrate prepared by a sintering method is filled with this alloy powder.

[0005]

By using the above composition and the above-mentioned sintered foamed nickel, a hydrogen storage electrode having a large discharge capacity and excellent discharge voltage characteristics can be obtained. First, by setting the ratio of Lm and Ni-Al-Co-M to the above range and at the same time setting the La amount in Lm to the above range, the gap between the unit lattices becomes large and the movement of hydrogen atoms becomes easy. Seem. Further, La in Lm on the surface easily becomes lanthanum hydroxide in the alkaline solution, and a porous alloy layer of nickel or cobalt is formed, so that hydrogen moves easily near the surface. In an alloy having an oxygen content of 0.05 wt% or more and 0.3 wt% or less, an oxide layer exists in the number of surface layers of about 1000Å. It is considered that these oxygens are mainly bonded to Al and Lm, and when they react with an alkaline solution, they are considered to form a more porous Raney nickel layer having a large specific surface area. In addition, nickel foam by the Ni powder sintering method, compared with nickel foam by the plating method, punching metal, three-dimensional substrate by the fiber sintering,
Since the surface of the current collector is uneven, the current collection characteristics are excellent. An excellent hydrogen storage electrode can be provided by filling the foamed nickel produced by sintering the Ni powder with the alloy having the above composition range.

[0006]

EXAMPLES Examples of the present invention will be described. Example 1 A hydrogen storage alloy having the composition shown in Table 1 was produced using an arc melting furnace. The alloy was crushed in a stainless steel bee in an argon atmosphere to obtain an alloy powder larger than 200 mesh and smaller than 440. By holding a part of this alloy powder in steam at 100 ° C. for 1 hour, the alloy surface was oxidized to obtain an alloy powder containing about 0.1 wt% oxygen. On the other hand, the nickel foam produced by the sintering method is immersed in a suspension liquid obtained by dispersing polyurethane powder in an aqueous solution containing nickel powder and a cellulosic binder, and then immersing it in a reducing atmosphere.
It was obtained by decomposing the polyurethane and simultaneously sintering the nickel powder by heating to 00 ° C.

As the hydrogen storage electrode, an alloy powder which was subjected to an oxidation treatment and an alloy powder which was not treated were mixed and kneaded with a 2 wt% polyvinyl alcohol aqueous solution to form a paste, and the nickel foam obtained by the above method was filled. Air dry this,
It was pressed to form a hydrogen electrode used for charging and discharging. Sintered Ni electrodes obtained by an ordinary method were placed on both sides of this hydrogen electrode via nylon separators, pressed from both sides with acrylic plates, immersed in a 30% KOH aqueous solution, and charged and discharged. The discharge current is 20 mA / g. The result is the discharge capacity shown in Table 1. This discharge capacity shows the values when the final voltage (F.V) is 1.0V and 0.8V. Alloy No. 1 is AB ₅
It is an example of a shape. Alloys No. 2 and No. 3 are examples of conventional AB _{2 type} . No. 1 has a final voltage of F.I. There was not much difference at V = 0.8V, and the discharge capacity was small. No. 2 and No. 3 are F. At V = 0.8V, the capacity is about 30% larger than that of No. 1. 10% at V = 1.0V
The capacity is only increasing. In contrast,
The alloys of No. 4 to No. 15 which are the products of the present invention are F. V = 0.
At 8 V, it is almost the same as the conventional AB _{2 type} ,
When V = 1.0V, the discharge capacity is increased by about 20%. On the other hand, in the case of the alloy No. 1 in the hydrogen storage electrode using the oxidized alloy powder, it did not change much depending on the presence or absence of the oxidation treatment. On the contrary, in alloys No. 2 and No. 3, the discharge capacity decreased. This is probably because zirconium or titanium was oxidized to form an oxide layer that was difficult to dissolve in an alkaline solution. However, in No. 4 to No. 15 alloys, F.I. The capacity at V = 0.8 V does not change significantly with or without oxidation treatment, but At V = 1.0, the capacity was further increased by about 20% as compared with the case without oxidation treatment. Thus, a hydrogen storage electrode having a large discharge capacity could be obtained.

Example 2 The discharge capacity when the electrode using the alloy with oxidation treatment of Example 1 was discharged (F.V = 1.0 V) at the discharge current of 200 mA / g of Example 1 is shown in Table 2. It was shown to. The alloys Nos. 4 to 15, which are the products of the present invention, were about 250 mAh / g to 300 mAh / g, and the conventional products were 220 mAh / g or less, and the effect of the products of the present invention was remarkable. In particular, in the case of electrodes using the hydrogen storage alloys with compositions No. 4 to No. 6,
A discharge capacity of 0 mAh / g or more was obtained. This is thought to be due to a slight difference in the stoichiometry in the hydrogen storage alloy and the influence of the constituent elements, but the details are not clear.

<Example 3> A hydrogen storage alloy was produced in the same manner as in Example 1 except that the La content in Lm was changed based on the composition of the No. 4 alloy. Hereinafter, the experimental method is the same as in Example 1. The results are shown in Fig. 1. When the La amount is 40 mol% or less, the discharge capacity when the final voltage is 1.0 V is smaller than when it is 40 mol% or more. Also, La
It was found that when the amount was 70 mol% or more, cycle life characteristics were deteriorated due to repeated charging and discharging. The cycle life here indicates a value when the initial capacity is reduced to 60%. Thus, the amount of La in Lm is 4
It is desirable to be 0 mol% or more and 70 mol% or less. N
Similar results were obtained for No. 6 and No. 8, and the La amount in the above range was effective.

<Example 4> Using No. 4 alloy powder,
A hydrogen storage electrode was produced in the same manner as in Example 1 except that the degree of oxidation treatment was changed. The oxygen content of the powder pulverized in an argon atmosphere was 0.005 wt%, and the oxygen content of the alloy was changed by changing the time of holding this in water vapor at 100 ° C. FIG. 2 shows the relationship between the oxygen content and the discharge capacity. A is F. V = 0.8 V discharge capacity, B = F. V
= 1.0 V discharge capacity. If it exceeds 0.4 wt% of the oxygen content, the discharge capacity sharply decreases.
This is probably because the oxide layer of the alloy powder becomes too thick. When the oxygen content is 0.005 wt%, the F. V =
At 1.0 V, the capacity is greatly reduced. In this way, V =
In order to obtain a hydrogen storage electrode having a large discharge capacity even at 1.0 V, the oxygen content of the alloy must be 0.05 wt% or more and 0.3 wt% or less.

<Embodiment 5> Various current collecting substrates were manufactured as follows. Foamed nickel powder obtained by sintering nickel powder is prepared by suspending nickel powder manufactured by Inco in a cellulosic aqueous solution, immersing the polyurethane sheet in it, and drying and then removing the polyurethane heated to 900 ° C. Is sintered to obtain a current collecting substrate. The plating type foamed nickel was vapor-deposited with carbon on polyurethane, then nickel-plated, and then heated to 900 ° C. to remove the polyurethane. The substrate obtained by sintering nickel fiber has a thickness of 50 μm and a length of 30 mm.
The substrate was sintered at 00 ° C. The punching metal used was a commercially available nickel-plated iron punching metal. Powder of alloy No. 4 was added to these current collecting substrates in an amount of 0.1 wt.
% Oxidation, kneading with a 2 wt% aqueous solution of polyvinyl alcohol, filling a three-dimensional substrate such as foamed nickel, and coating it on the punching metal of the two-dimensional substrate to obtain a hydrogen storage electrode.
The test cell is the same as in Example 1. The results are shown in Table 3.
In the case of nickel foam by sintering, the F. The discharge capacity of V = 1.0V was large. When the surface of the current collecting substrate was observed, the surface of the nickel foam formed by sintering had many irregularities, and that by the plating method had few irregularities. There were almost no irregularities in the sintered nickel fiber or punched metal. From these, it is considered that the unevenness of the current collecting substrate is involved as a factor for improving the discharge characteristics.

Example 6 Alloy No. 4 and primary particle size 3 were added to nickel foam obtained by sintering with a thickness of 1 mm.
The slurry was filled with a slurry mixed with nickel powder of μm, air-dried, and then pressed to make the thickness of the electrode 0.4 mm. Charging and discharging were performed under the same conditions as in Example 1, and F.I. It was set to V = 1.0V. Table 4 shows the number of times of charge and discharge until the capacity reaches 95% of the maximum capacity of the electrode and the discharge capacity per unit volume.
When the amount of nickel powder added is 3 wt% or less, the activation of the alloy is slow, and the capacity cannot reach 95% or more of the maximum capacity unless the charge and discharge are repeated 7 times or more. In the case of actually making a sealed battery, if the activation is slow, the balance between the nickel electrode and the hydrogen storage electrode will be lost, and hydrogen gas will be generated from the hydrogen storage electrode, which is a major drawback. An electrode containing 5 wt% or more of nickel powder reaches 95% of the maximum capacity after three or two charge / discharge cycles. However, if the amount of nickel powder added is large, the discharge capacity per unit volume will decrease. In the case of actually making a sealed battery, even if the discharge capacity per unit weight of the alloy is large, if the discharge capacity per unit volume is not large, it cannot be put in the predetermined size. From these results, by adding the nickel powder in the range of 5 wt% or more and 15 wt% or less, the discharge capacity becomes large,
It was found that an electrode with fast activation can be obtained.

<Example 7> The primary particle diameter is 1, 2, 3,
Example 6 was added with 10 wt% of nickel powder of 5,7 μm.
It was used as an electrode. FIG. 3 shows the discharge capacity density per unit volume at this time. When the nickel powder of 1 μm was added, a larger amount of solvent was required as compared with the case of the nickel powder of 2-3 μm, and the volume density when filled was decreased. Even when pressed, it was about 100 mAh / ml smaller than the value when nickel powder of 2-3 μm was added.
On the other hand, with the 5.7 μm nickel powder, it was considered that the discharge capacity density per unit volume was lowered because the nickel powder could not completely fill the gap between the alloys. 2,3μ
In the case of nickel powder of m, since it enters the gap between the alloy powders and takes the closest packing structure, the amount of solvent can be small,
It seems that the discharge capacity density is maximized.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

[Table 4]

[0018]

As described above, the hydrogen storage alloy and the hydrogen storage electrode according to the present invention have the composition formula LmNi _a Co _b Al.
_{In C} M _d , the amount of La in Lm is 40 to 70 mol%, and the range of a, b, c, d is 1.2 ≦ a ≦ 1.6,0.
1 ≦ b ≦ 0.4, 0.05 ≦ c ≦ 0.1, 0.1 ≦ d ≦
0.3, 1.8 ≦ a + b + c + d ≦ 2.4, and M in the composition formula is at least one hydrogen storage alloy of Mn, Cu, Zn, In, Sn, and Pb, and its alloy powder Since the oxygen content is 0.05 wt% or more and 0.3 wt% or less and the hydrogen storage alloy powder is filled in the nickel foam sintered nickel foam, the discharge capacity is higher than that of the conventional hydrogen storage electrode. It is large and excellent in that the discharge voltage is high.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of the amount of La in Lm on discharge capacity and charge / discharge cycle life.

FIG. 2 is a diagram showing a relationship between oxygen content in an alloy and discharge capacity.

FIG. 3 is a graph showing the influence of the primary particle shape of nickel powder on the discharge capacity density.

Claims (4)

[Claims] 1. In the composition formula LmNi _a Co _b Al _c M _d , Lm represents La-rich Mm, the amount of La in this Lm is 40 to 70 mol%, and the range of a, b, c, d is 1.2 ≦ a ≦ 1.6, 0.1 ≦ b ≦ 0.4, 0.05
≦ c ≦ 0.1, 0.1 ≦ d ≦ 0.3, 1.8 ≦ a + b +
c + d ≦ 2.4, and M in the composition formula is Mn, Cu, Z
Hydrogen storage alloy of at least one of n, Ag, In, Sn and Pb, wherein the oxygen content of the alloy powder is 0.05 wt% or more and 0.3 wt% or less alloy. 2. The hydrogen storage alloy according to claim 1, wherein the range of 1.85 ≦ a + b + c + d ≦ 2.0 and M is Mn. 3. A hydrogen storage electrode, characterized in that foamed nickel obtained by a sintering method of nickel powder is filled with the hydrogen storage alloy according to claim 1. 4. The primary particle size of the hydrogen storage alloy is 2 μm.
The hydrogen storage electrode according to claim 3, wherein 5 to 15 wt% of nickel powder of m or more and 3 μm or less is added.